1. Field of the Invention
The present invention relates to an aging device usable in a method for manufacturing a plastic molded product part. More particularly, the present invention relates to an aging device in which a die for aging can be uniformly and rapidly heated and cooled and a cooling speed of the die for aging can be easily controlled and the die for aging can be easily manufactured at low cost.
The present invention also relates to a method for manufacturing a plastic molded product and used in an optical scanning system such as a laser beam printer, a facsimile telegraph, etc. and a video camera, etc. More particularly, the present invention relates to a method for suitably manufacturing a plastic molded product such as a large-sized long plastic lens, etc.
The present invention further relates to a method and an apparatus for manufacturing a plastic mirror requiring a mirror face with high accuracy.
2. Description of the Related Art
In a general known method for manufacturing a plastic molded product, a plastic base material is approximately processed in a final shape by injection molding in advance. Thereafter, this plastic base material is inserted into a die having a plurality of cavities. Next, this plastic base material is heated and melted until a temperature equal to or higher than a transition point of glass so that an internal pressure of resin is caused. Next, the plastic base material is gradually cooled to transfer a mirror face. In this manufacturing method, injecting and aging processes of the plastic molded product are separated from each other as mentioned above.
In this manufacturing method of the plastic molded product, it is important to rapidly heat and cool the plastic base material in the aging process and uniformly control a temperature within the die.
An aging device having the above aging process has a heating section for heating the plastic base material and a cooling section for cooling the plastic base material. In the heating section, a plurality of heaters are buried into the die for aging. In the cooling section, a plurality of heat pipes arc buried into the die for aging. The plastic base material is heated by the plural heaters buried in the heating section. The plastic base material is cooled by the plural heat pipes buried in the cooling section. In particular, in the case of cooling, a refrigerant such as water, oil, etc. flows through an exposure portion from the die of the heat pipes. A flow rate of this refrigerant is adjusted to suitably control a cooling speed of the die. A fin is attached to the exposure portion. The cooling speed is also suitably controlled by adjusting an amount of air sent to the fin.
However, in the above general aging device, the die for aging is cooled in the cooling section in which the plural heat pipes are buried into the die for aging. Accordingly, the flow rate of the refrigerant is excessively large so that no flow speed of the refrigerant can be increased. Therefore, no heat exchange of the refrigerant can be sufficiently performed so that it is impossible to rapidly cool the die for aging and precisely control the cooling speed of the die for aging. Further, the refrigerant temperature is changed in the vicinity of inflow and outflow ports of the refrigerant. Therefore, heat exchange efficiencies of heat pipes near the inflow and outflow ports are changed so that no die can be uniformly cooled in a certain case.
Further, when a heat pipe is arranged in the die, the heat pipe tends to be damaged. Therefore, no heat pipe can be press-fitted into the die so that a clearance is caused between the die and the heat pipe. Accordingly, there is a case in which cooling efficiency of the heat pipe is reduced by heat loss caused by this clearance.
When a heating speed of the die is increased by heating a heater, heating overshoot tends to be caused so that the die for aging is excessively heated or it takes much time to heat the die for aging in a certain case.
Since heaters and heat pipes are arranged within the die for aging in the general aging device, it is necessary to manufacture and arrange another die for aging having these heaters and heat pipes in accordance with a change in molded product object. Accordingly, it takes time and labor to manufacture the die and manufacturing cost of the die is increased in a certain case.
It is therefore an object (as a first object) of the present invention to provide an aging device in which a die for aging can be uniformly and rapidly heated and cooled and a cooling speed of the die for aging can be easily controlled and the die for aging can be easily manufactured at low cost.
In an injection-molding operation of a molded resin product such as a plastic lens, the plastic lens, etc. are generally obtained with high accuracy by cooling all resins from a temperature equal to or higher than a transition temperature of glass. In this case, it is difficult to obtain a molded product having no contraction, etc. with reduced residual stress unless the molded product is gradually cooled in a state of a temperature difference of several ten degrees from at least the temperature equal to or higher than the glass transition temperature to a temperature equal to or lower than a load flexing temperature. In the case of a plastic lens, it is difficult to obtain a molded lens product having small birefringence unless the molded lens product is gradually cooled in such a state.
It is necessary to cool the die so as not to cause this contraction, etc. while a temperature of the die filled with resin having a low coefficient of thermal conductivity is uniformed as much as possible. Therefore, various kinds of cooling devices are arranged in the die for molding the plastic product to cool this die.
For example, FIG. 41 shows a general cooling device. In FIG. 41, each of reference numerals 1 and 2 designates a die plate of a hydraulic press machine. Heating-cooling members 5 and 6 are respectively attached to the die plates 1 and 2 through heat insulating materials 3 and 4. A die 7 for plastic molding is attached to the heating-cooling members 5 and 6. This die 7 is constructed by a pair of divisional dies 8 and 9 opposed to each other. The divisional dies 8 and 9 form at least one cavity and have at least one mirror face.
A plurality of heaters 10 and 11 are respectively buried into the heating-cooling members 5 and 6. The heaters 10 and 11 are connected to an unillustrated heating source. The die 7 is heated by heating the heaters 10 and 11 by this heating source. An unillustrated cooling passage is formed in each of the heating-cooling members 5 and 6. A refrigerant such as water, oil, etc. is supplied from a refrigerant temperature regulator 13 to an end portion of this cooling passage through a plurality of pipe lines 12.
A thermoplastic base material is preprocessed in a final shape in advance and is inserted into the cavity of the above die 7. Thereafter, the die 7 is heated to a temperature equal to or higher than a glass transition temperature of the plastic base material by heating the heaters 10 and 11. Thus, the plastic base material is melted and a predetermined resin pressure is generated within the cavity so that a mirror face is transferred to the plastic base material. Next, the die 7 is gradually cooled by supplying the refrigerant to the cooling passage through the pipe lines 12. When the temperature of the die 7 is reduced to a temperature equal to or lower than a thermal deforming temperature of resin, the plastic base material is taken out of the cavity so that the plastic base material is molded as a plastic molded product.
For example, Japanese Patent Application Laying Open (KOKAI) No. 61-279515 shows a general example about another cooling structure. In this cooling structure, a plurality of heat pipes are buried into a die and a heating member is attached to each of the heat pipes. Further, a cooling passage is disposed within the die such that the cooling passage extends over the plural heat pipes. A cooling portion able to exchange heat of a refrigerant such as cooling water, etc. is disposed in a portion of the heat pipes. The cooling portion and the cooling passage of the die are set to be in conformity with each other so that the cooling refrigerant is supplied to the cooling passage through the pipe lines. The heat pipes are cooled by this cooling refrigerant so that the die is cooled through the heat pipes.
However, the plural pipe lines 12 are connected to the cooling passages of the heating-cooling members 5 and 6 in the former die 7 for plastic molding. Accordingly, there is a problem that operability of the die 7 is very reduced when the die 7 is opened and closed. Further, no material of the die 7 is especially considered so that no die 7 can be cooled uniformly and rapidly, thereby reducing cooling efficiency of the die 7.
In the latter die for injection molding, a plurality of pipe lines are also connected to the cooling passage of the die. Accordingly, operability of the die is very reduced when the die is opened and closed. Further, it is necessary to mold the cooling passage in addition to holes for burying the heat pipes so that manufacturing cost of the die is increased. Further, no material of the die is especially considered and the cooling passage is arranged such that the cooling passage extends over the plural heat pipes. Therefore, no die can be cooled uniformly and rapidly and it is difficult to control and adjust a temperature of the die so that cooling efficiency of the die is reduced.
The pipe lines are arranged in the above two dies for plastic molding and injection molding. Accordingly, diameters of these pipes are reduced by rust, dirt, etc. so that cooling efficiency of each of the dies is reduced. Therefore, it is necessary to clean the pipe lines so that a maintenance operation of the pipe lines is additionally required.
Another object (as a second object) of the present invention is to provide a device for cooling a die for plastic molding in which a cooling speed of the die can be easily controlled while the die is cooled uniformly and rapidly, and cooling efficiency of the die can be improved and pipe lines for cooling are removed from the die so that operability of the die can be improved when the die is opened and closed.
For example, Japanese Patent Application Laying Open (KOKAI) No. 4-163119 shows a general method for manufacturing a plastic molded product. This manufacturing method has an injection molding process and an aging process. In the injection molding process, predetermined resin is heated to a temperature equal to or higher than a fluidizable temperature at which this resin can be fluidized. The resin is then injection-molded into a die held at a temperature equal to or lower than a thermal deforming temperature of this resin. A gate seal is next formed. In the aging process, the die filled with the above resin is heated such that the temperature of the above injection-molded resin is equal to or higher than a glass transition temperature of this resin. The die is then held for a predetermined time at the temperature equal to or higher than the glass transition temperature. The die is next gradually cooled until the temperature of the above resin is equal to or lower than the thermal deforming temperature of the resin. Since the manufacturing method has the above injection molding process and the above aging process, the die temperature can be set to be equal to or lower than the thermal deforming temperature of the resin.
For example, a general die for aging is shown in Japanese Patent Application No. 3-33130. In this patent application, the die for aging is constructed and manufactured by a material having a preferable coefficient of thermal conductivity. Accordingly, heating and cooling times of the die can be reduced so that throughput can be improved. Further, yield can be improved by approximately cooling the die uniformly at a cooling time thereof.
For example, Japanese Patent Application No. 4-29119 shows a general plastic molding machine. In this patent application, at least one of dies for aging is set to a separating die able to be separated into a plurality of die members around a cavity as a center. This separating die can be clamped by a die clamping mechanism from both sides of the separating die. Accordingly, a plastic base material can be easily inserted and molded into the cavity and can be easily taken out of the cavity as a molded product. Accordingly, the plastic base material can be molded in a desirable shape without distorting and damaging the molded product.
In a general method for taking the molded product out of the die in the plastic molding machine, the molded product is projected outward by using an ejector pin, an ejector sleeve, etc. Otherwise, the molded product is separated from the die by using a stripper plate. When a plurality of molded products are taken out of the die, the plural molded products projected out by the above taking-out method are connected to each other through a runner and a sprue. Accordingly, the molded products can be easily and simultaneously taken out of the die.
In a method for manufacturing a plastic molded product such as a lens, a mirror, etc. with high accuracy, a plastic base material is approximately processed in a final shape by injection molding in advance. Thereafter, the plastic base material is inserted into a die having a plurality of cavities. The plastic base material is next heated and melted until a temperature equal to or higher than a glass transition point so that an internal pressure of resin is generated. Next, the plastic base material is gradually cooled and a mirror face is transferred. In this manufacturing method, injecting and aging processes are separated from each other as mentioned above.
However, in an aging device of this general molding machine, no gate is formed in molded products inserted and taken out of the aging die. The molded products are individually separated from each other. Accordingly, no plural molded products can be simultaneously inserted and taken out of the aging die. Further, it takes much time to insert and take each of the plural molded products out of the aging die one by one. Accordingly, a cyclic time of the aging process is increased so that merits of the aging process are reduced even when many molded products are taken out of the aging die.
Another object (as a third object) of the present invention is to provide an aging device for reducing the cyclic time of an aging process.
As mentioned above, the manufacturing method of a plastic molded product shown in the above Japanese Patent Application Laying Open (KOKAI) No. 4-163119 divisionally has an injection molding process and an aging process. In the injection molding process, a resin base material is injected into a die for injection molding and is approximately preprocessed in a final shape. In the aging process, the preprocessed resin base material is inserted and heated within a cavity of the die for aging. Thereafter, the resin base material is gradually cooled.
Since this manufacturing method has the divided injection-molding and aging processes, the injection-molding and aging processes can be designed such that these processes are suitable for molding processing. Further, the number of taking-out operations of the die in the aging process can be set to be larger than that in the injection molding process. Accordingly, it is possible to perform many aging operations by using one aging die.
However, in this manufacturing method of a plastic molded product divisionally having the injection-molding and aging processes, the molded product constructed by only a resin material is simply manufactured. Accordingly, in this manufacturing method, no hybrid molded product as a molded product formed by combining this resin material with a different material is manufactured with high accuracy. Therefore, it is desirable to provide a method for manufacturing a molded product usefully using each of material characteristics.
Another object (as a fourth object) of the present invention is to provide a method for manufacturing a molded product in which an integral molded product can be manufactured with high accuracy by melting and joining resin with a material of a different kind, and a molded product usefully using different material characteristics can be obtained by suitably selecting used materials and a degree of freedom in design of the molded product can be increased. In this manufacturing method, a material of at least one kind different from resin is combined with resin in an aging process and is injected into an aging die set such that a resin temperature is equal to or higher than a glass transition temperature. Thereafter, the combined resin material is held for a predetermined time at a temperature equal to or higher than the glass transition temperature and is gradually cooled to a temperature equal to or lower than a thermal deforming temperature of the resin.
Another object (as a fifth object) of the present invention is to provide a method for manufacturing a molded product in which a material of at least one kind among aged materials is made of thermoplastic resin so that the plural materials can be easily integrated with each other in a melting state of resin and a mirror face can be easily transferred to resin.
Another object (as a sixth object) of the present invention is to provide a method for manufacturing a molded product in which an aging temperature of an aging die is set to be equal to or higher than a lowest glass transition temperature of combined resin materials so that the resin materials can be rapidly melted and integrated with each other and an aging time can be reduced.
Another object (as a seventh object) of the present invention is to provide a method for manufacturing a molded product having a high quality in which a taking-out temperature of an aging die for aging is set to be equal to or lower than a lowest glass transition temperature of combined resin materials so that different materials are cooled and reliably integrated with each other and can be then taken out of the aging die.
Another object (as an eighth object) of the present invention is to provide a method for manufacturing a molded product having a high quality in which a cavity of an aging die is set to be in a vacuum state at an aging time so as to prevent air bubbles from being mixed and flowed to a central portion of joining faces of materials in an aging process so that it is possible to prevent air bubbles from being mixed and flowed into a central portion of the molded product formed by integrating these materials with each other.
As mentioned above, the general manufacturing method of a plastic molded product in Japanese Patent Application Laying Open (KOKAI) No. 4-163119 divisionally has an injection molding process and an aging process. In the injection molding process, resin is heated to a temperature equal to or higher than a fluidizable temperature of resin at which this resin can be fluidized. The resin is then injected into a die held at a temperature equal to or lower than a thermal deforming temperature of this resin so that the resin is approximately preprocessed in a final shape. In the aging process, the preprocessed resin material is flowed into a cavity of the aging die and is held for a predetermined time at a temperature equal to or higher than a glass transition temperature of the resin. Thereafter, the resin material is gradually cooled to a temperature equal to or lower than a thermal deforming temperature of the resin.
Since this manufacturing method has the divided injection-molding and aging processes, the injection-molding and aging processes can be designed such that these processes are suitable for molding processing. Further, the number of taking-out operations of the die in the aging process can be set to be larger than that in the injection molding process. Accordingly, it is possible to perform many aging operations by using one aging die as mentioned above.
However, in this method for manufacturing a plastic molded product by dividing into the injection molding process and the aging process, it is necessary to dispose a large-sized injection molding machine to obtain a molded product which is large-sized and long.
Namely, a large force for clamping the die is required in the injection molding process since a large pressure of melted resin is caused when the melted resin is injected into the die to fill the die with the melted resin. Therefore, a large-sized injection molding machine for applying the large clamping force to the die is required to form a molded product which is large-sized and long. In contrast to this, the clamping force of the die may be set to be small in the aging process since only an internal pressure is generated by thermal expansion of resin caused by an increase in temperature of the aging die. Accordingly, the large-sized molding machine is required to manufacture a large-sized long molded product although no large-sized aging die is required. Therefore, manufacturing cost of the molded product is very increased.
Further, cavities of the injection molding die and the aging die have the same shape to form the same molded product. Accordingly, a molded product having a shape of only one kind can be manufactured. Therefore, it is impossible to sufficiently cope with mass production of many kinds increased in the future by the same die.
Another object (as a ninth object) of the present invention is to provide a method for manufacturing a plastic molded product at low cost in which a resin base material approximately preprocessed in a final shape by injection molding is divided into two divisional portions or more so as to mold the resin base material twice or more so that clamping force of a die can be reduced at each of injection molding times, and a large-sized long molded product can be easily manufactured by a compact molding machine.
Another object (as a tenth object) of the present invention is to provide a method for manufacturing a plastic molded product in which no divisional direction of a resin base material approximately preprocessed in a final shape is set to be parallel with a parting face of an aging die so that clamping force of the die can be further reduced at an injection molding time.
Another object (as an eleventh object) of the present invention is to provide a method for manufacturing a plastic molded product in which resin base materials are joined with each other and are easily formed in a shape for providing different thicknesses of the resin base materials, and it is possible to prevent contraction of the molded product from being caused in the formation of the resin base materials.
Another object (as a twelfth object) of the present invention is to provide a method for manufacturing a plastic molded product in predetermined shapes of many kinds.
Another object (as a thirteenth object) of the present invention is to provide a method for manufacturing a plastic molded product having a high quality in which it is possible to prevent air bubbles from being mixed and flowed to a central portion of joining faces of resin base materials in an aging process so that it is possible to prevent air bubbles from mixed and flowed into a central portion of the molded product formed by integrating the resin base materials with each other.
Another object (as a fourteenth object) of the present invention is to provide a method for manufacturing a plastic molded product having a high quality in which it is possible to prevent air bubbles from being mixed and flowed to a central portion of joining faces of resin base materials in an aging process by setting a cavity of an aging die to be in a vacuum state in the aging process so that it is possible to prevent air bubbles from being mixed and flowed into a central portion of the molded product formed by integrating the resin base materials with each other.
In general, many kinds of a polygon mirror, an f.theta. mirror, etc. are used to perform an optical scanning operation of a laser printer, a copying machine, etc. However, manufacturing amounts of the polygon mirror, the f.theta. mirror, etc. are small. Therefore, the polygon mirror, the f.theta. mirror, etc. are constructed by plastic materials in many cases. However, a mirror face having a high accuracy has been recently required for the polygon mirror, the f.theta. mirror, etc. in accordance with high processing speed and high density of information.
In a method for manufacturing a plastic mirror of this kind, a mirror face of a die having a high accuracy is transferred by injection molding, injection-compression molding, etc. Thereafter, a predetermined metal is directly evaporated to a transferred mirror face portion of a molded product so that a metallic reflecting film is formed as a mirror face. The mirror face portion of the molded product is covered with MgF.sub.2, etc. as a ground to evaporate the metallic reflecting film so as to improve adhesion of the metallic reflecting film and the molded product. Further, a protecting film of SiO.sub.2, etc. is formed on a surface of the metallic reflecting film to improve a strength thereof. For example, such a plastic mirror manufacturing method is described in Japanese Patent Publication (KOKOKU) No. 61-25131 and Japanese Utility Model Application Laying Open (KOKAI) No. 59-116905.
Another plastic mirror manufacturing method is practically used. In this manufacturing method, a metallic reflecting film is formed on a plastic film. A portion of the plastic film on a side of the metallic reflecting film is adsorbed onto a mirror face of a die by suction, etc. Thereafter, resin is injection-molded on a rear side of the metallic reflecting film on the plastic film so that a mirror face is laminated. For example, such a plastic mirror manufacturing method is described in Japanese Patent Publication (KOKOKU) No. 4-9647 and Japanese Patent Application Laying Open (KOKAI) No. 62-224533.
However, in the plastic mirror manufacturing method using evaporation, a predetermined metal is directly evaporated to a mirror face portion by batch processing so that a mirror face is formed. Accordingly, cost of the plastic mirror is increased. Further, evaporation conditions must be changed every molded product since shapes of the plastic mirror are different from each other in accordance with uses. However, it is complicated to change in the evaporation conditions every molded product. Further, when the mirror face portion has irregularities, no metallic reflecting film can be uniformly formed.
In the manufacturing method of a plastic mirror using lamination, an apparatus for manufacturing the plastic mirror can be manufactured by only adding a slight arrangement to an existing injection molding machine with small investment. However, since melted resin is injected into a cavity adsorbing a plastic film, the plastic film is deformed with wrinkles, etc. at a high temperature and a fluidizing pressure when the melted resin is injection-molded. Accordingly, no mirror face having a high accuracy is obtained in this manufacturing method.
Accordingly, another object (as a fifteenth object) of the present invention is to provide a method and an apparatus for manufacturing a plastic mirror at low cost in which a plastic base material approximately processed in a final shape and having a mirror face portion, and a plastic film forming a metallic reflecting film thereon are inserted into a cavity and are heated and joined with each other at uniform temperature and pressure so that a mirror face of a die is transferred with high accuracy to manufacture a face of the plastic mirror having a high accuracy.